A pensioner and a mother from Melbourne, both caught with millions of dollars' worth of drugs bound for Australia, have had their charges dropped in a landmark ruling in Hong Kong after claiming they were the victims of sophisticated online scams.

Key points:

Two Australians caught carrying drugs at Hong Kong Airport before flight to Australia released

Charges dropped after prosecutors offered no evidence

Pair claim they are victims of sophisticated online scam

They and four others spent up to 19 months in jail

Joerg Ulitzka, 80, Suong Thu Luu, 44, and four others from the US, Ireland and the Netherlands were released by Hong Kong's High Court on Friday after prosecutors offered no evidence.

The six had spent up to 19 months behind bars, after each being caught with quantities of the drug ice between 1.6 and 4 kilograms as they boarded flights at Hong Kong Airport bound for Australia and New Zealand.

In releasing them, High Court judge Kevin Zervos criticised lengthy delays in the prosecution and called on law enforcement agencies to go after the "major miscreants behind the drug trade", who he described as "the evil ones".

He said dealing with drug trafficking "does not simply rest on the drug mules", who "may be victims too".

"Never have the words been truer than now, that justice delayed is justice denied," Judge Zervos said.